FIG. 1 shows a block diagram of a conventional power system 100 which includes a first power source, e.g., an adapter 102, and a second power source, e.g., a battery 110. The power system 100 further includes a direct-current to direct-current (DC/DC) converter 104, a charger 106, a switch 103, a switch 105, and a load, e.g., a light-emitting diode (LED) 108. The adapter 102 can be coupled to an AC power source (e.g., a 120V commercial power supply) and convert an AC voltage from the AC power source to a DC voltage VAD.
In operation, when the switch 103 is turned on and the switch 105 is turned off, the power system 100 operates in a battery charging process. The adapter 102 delivers the DC voltage VAD to charge the battery 110 and can also power the LED 108. The charger 106 provides proper charging power to the battery 110. The DC/DC converter 104 receives the DC voltage VAD and provides the LED 108 with regulated power. When the switch 105 is turned on and the switch 103 is turned off, the battery 110 provides power to the LED 108 via the DC/DC converter 104.
However, there are two power chains in the power system 100. One power chain includes the charger 106, and the other includes the DC/DC converter 104. These two power chains increase the power consumption of the power system 100, thereby reducing the system power efficiency. These two power chains also increase the complexity of the power system 100. In addition, with the use of both the charger 106 and the DC/DC converter 104, the size of the printed circuit board (PCB) may be relatively large, which increase the cost of the power system 100.